The present invention refers to an apparatus for feeding bulk material, in particular to a cellular wheel sluice or rotary feeder of the type including a housing provided with a top inlet and a bottom outlet and accommodating a rotor which includes a plurality of radial vanes supported on a horizontal shaft and including sealing strips which extend parallel to the shaft and abut the inner wall surface of the housing.
In such a feeding apparatus, it is desired to keep the amount of leakage air as low as possible. There are three locations where air may leak, that is the axial gap between the housing and the rotor, the radial gap between the housing and the rotor, and the scooped air volume of the rotor compartments. Thus, the amount of leakage air depends at given gap widths and given capacity of the compartments on the pressure drop between inlet and outlet as well as on the rotational speed of the rotor.
While scooped air losses have to be accepted, the amount of leakage air through the axial gap can be reduced by specially designed axial face seals. Further, the use of sealing strips extending along or in the end faces of the vanes were proposed for reducing the amount of leakage air escaping through the radial gaps. Such sealing strips, however, wear out relative quickly especially during transport of abrasive bulk material. Therefore, the device must be shut down within short periods and partly dismantled in order to adjust or replace the sealing strips.
The U.S. Pat. No. 3,556,355 describes a rotary feeding apparatus of this kind in which the sealing strips are automatically adjusted in order to compensate wear thereof. The vanes of the rotor are provided at their end faces with grooves which accommodate sealing strips guided for radial displacement and made of e.g. polytetrafluoroethylene. The grooves are connected via bores with a central passageway in the shaft of the rotor. Fluid under pressure is introduced through the passageway and the bores to the grooves so that the sealing strips are maintained in contact with the inner surface wall of the housing by a constant, pressure-dependent force.
This prior art has, however, some drawbacks which prevented its use in practice. There are considerable technical difficulties to guide the sealing strips sufficiently tight within the grooves especially at the corners of the vanes i.e. at the junction of the radial end face with the axial end face of a vane. Further, the degree of wear of the sealing strips cannot be monitored or controlled from outside. Also, an uneven wear over the length of the sealing strips and/or varying friction along the portion of the sealing strips arranged in the grooves of the vanes result in tilting or canting of the sealing strips.